Method for reporting channel state information, user equipment, and base station

ABSTRACT

Embodiments of the present invention provide a method includes: receiving a reference signal sent by a base station; selecting, based on the reference signal, a precoding matrix from a codebook, where a precoding matrix W included in the codebook is a product of three matrices being W1, Z, and W2, that is, W=W1ZW2, where both W1 and Z are block diagonal matrices, W1=a formula (I), Z=a formula (II), each of W1 and Z includes at least one block matrix, that is, NB≥1, and each column of each block matrix Zi in the matrix Z has the following structure formula (III); and sending a precoding matrix indicator PMI to the base station, where the PMI corresponds to the selected precoding matrix, and is used by the base station to obtain the selected precoding matrix W according to the PMI.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/594,646, filed on Oct. 7, 2019, which is a continuation of U.S.patent application Ser. No. 16/058,636, filed on Aug. 8, 2018, now U.S.Pat. No. 10,447,356, which is a continuation of U.S. patent applicationSer. No. 15/808,318, filed on Nov. 9, 2017, now U.S. Pat. No. 10,063,296on Aug. 28, 2018, which is a continuation of U.S. patent applicationSer. No. 15/439,686, filed on Feb. 22, 2017, now U.S. Pat. No. 9,838,097on Dec. 5, 2017, which is a continuation of U.S. patent application Ser.No. 14/883,334, filed on Oct. 14, 2015, now U.S. Pat. No. 9,608,708 onMar. 28, 2017, which is a continuation of International Application No.PCT/CN2013/074214, filed on Apr. 15, 2013. All of the afore-mentionedpatent applications are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to the field of communicationstechnologies, and in particular, to a method for reporting channel stateinformation, user equipment, and a base station.

BACKGROUND

In a multiple input multiple output (MIMO) system, to eliminateco-channel interference caused by multiple users and multiple antennas,some necessary signal processing technologies need to be used at twoends of a transceiver, so as to improve communication performance of thesystem.

In the prior art, a precoding technology is proposed. A major principleof the precoding technology is that a base station uses known channelstate information (CSI) to design a precoding matrix for processing asent signal, so as to reduce interference on the sent signal. A MIMOsystem using precoding may be represented as follows:

y=HVs+n

where Y is a received signal vector, H is a channel matrix, V is aprecoding matrix, s is a transmitted symbol vector, and n is aninterference and noise vector.

Optimal precoding usually requires that a transmitter entirely knowschannel state information (CSI). In a common method, a terminalquantizes instantaneous CSI and feeds back the instantaneous CSI to abase station (BS).

In an existing long term evolution (LTE) R8 system, CSI information fedback by a terminal includes information such as a rank indicator (RI), aprecoding matrix indicator (PMI), and a channel quality indicator (CQI),where the RI and the PMI respectively indicate a used layer quantity anda used precoding matrix. A set of used precoding matrices is generallyreferred to as a codebook, where each precoding matrix is a code word inthe codebook. An existing LTE R8 4-antenna codebook is designed based ona Householder transformation, and a code word of the codebook may becompatible with a uniform linear array antenna configuration and a crosspolarization antenna configuration. Double-codebook design for 8antennas is introduced in an LTE R10 system, and quantization accuracyis further improved without excessively increasing feedback overheads.

On one hand, the foregoing LTE R8 to R10 codebooks are mainly designedfor a macro cell system. A position of a base station or a transmitteris usually higher than the height of a surrounding building (forexample, the height of an antenna is approximately between 200 to 250feet); therefore, a major transmission path of the base station or thetransmitter is higher than a roof, and a transmitted multipath componentusually surrounds a direction of a line of sight (Line of Sight, LOS forshort). In this way, each multipath component is usually located withina plane in which the line of sight is located, that is, angle extensionin a pitch angle direction approaches 0. On the other hand, theforegoing codebooks are designed based on a conventional base stationantenna; for the conventional base station antenna, a perpendicularantenna beam having a fixed tilt angle is used, but only a direction ofa horizontal beam can be adjusted dynamically.

However, to conform to user density and a data service demand that areincreasing rapidly, and to further reduce transmit power, the concept ofmicro cell is further introduced. A position of a base station or atransmitter in a micro cell system is usually lower than the height of asurrounding building (for example, an antenna is installed on a lamppostin a street, and usually is at a height of approximately 30 feet), and awireless transmission mechanism of the micro cell system is obviouslydifferent from the foregoing macro cell environment, where somemultipath components may surround a LOS direction, and some othermultipath components are probably along the ground or the street. Thisdouble-transmission mechanism causes larger angle extension, especiallyin a direction of a pitch angle, which is obviously different from themacro cell. Currently, design of LTE R8-R10 codebooks cannot be welladapted to the foregoing micro cell environment.

In addition, to further improve spectrum efficiency, currently, in anLTE R12 standard to be launched, introduction of more antennaconfigurations, especially an antenna configuration based on an activeantenna system (AAS), starts to be considered. Different from aconventional base station, an AAS base station further provides freedomin designing an antenna in a perpendicular direction, which is mainlyimplemented by using a two-dimensional antenna array in horizontal andperpendicular directions of the antenna; the conventional base stationactually uses a horizontal one-dimensional array, although each antennaport in a horizontal direction of the antenna may be obtained byperforming weighting on multiple array elements in a perpendiculardirection. Currently, the design of the LTE R8-R10 codebooks cannot bewell adapted to the foregoing antenna configuration.

SUMMARY

Embodiments of the present invention provide a method for reportingchannel state information, user equipment, and a base station. In aprecoding matrix indicated in the channel state information reported bythe user equipment, a channel characteristic of a double-transmissioncondition in a micro cell network environment and freedom in horizontaland perpendicular directions of an antenna of an AAS base station areconsidered, which can improve communication performance of the microcell network environment and an AAS base station system.

To achieve the foregoing objective, the following technical solutionsare used in the embodiments of the present invention:

According to a first aspect, an embodiment of the present inventionprovides a method for reporting channel state information, where themethod includes:

receiving a reference signal sent by a base station;

selecting, based on the reference signal, a precoding matrix from acodebook, where a precoding matrix W included in the codebook is aproduct of three matrices being W₁, Z, and W₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag{Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, andβ_(i,k)≥0; and

sending a precoding matrix indicator PMI to the base station, where thePMI corresponds to the selected precoding matrix, and is used by thebase station to obtain the selected precoding matrix W according to thePMI.

In a first possible implementation manner, with reference to the firstaspect, the selecting, based on the reference signal, a precoding matrixfrom a codebook specifically includes:

selecting, based on the reference signal, the precoding matrix from acodebook subset, where the codebook subset is a subset predefined, ornotified by the base station, or reported by user equipment.

In a second possible implementation manner, with reference to the firstpossible implementation manner, the codebook subsets share at least onesame matrix subset of the following matrix subsets: subsets of a matrixW₁, a matrix W₁Z, a matrix W₂, a matrix ZW₂, and a matrix Z.

In a third possible implementation manner, with reference to the firstaspect or the first and second possible implementation manners, thesending a precoding matrix indicator PMI to the base stationspecifically includes:

sending a first precoding matrix indicator PMI₁ and a second precodingmatrix indicator PMI₂ to the base station, where the PMI₁ is used toindicate the matrix W₁Z, and the PMI₂ is used to indicate the matrix W₂;or

sending a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ to the base station, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;or

sending a second precoding matrix indicator PMI₂, a third precodingmatrix indicator PMI₃, and a fifth precoding matrix indicator PMI₅ tothe base station, where the PMI5 is used to indicate the matrix Z.

In a fourth possible implementation manner, with reference to the thirdpossible implementation manner, the sending a precoding matrix indicatorPMI to the base station specifically includes:

sending the PMI₁ to the base station according to a first period; and

sending the PMI₂ to the base station according to a second period, wherethe first period is greater than the second period; or

sending the PMI₃ to the base station according to a third period; and

sending the PMI₄ to the base station according to a fourth period, wherethe third period is greater than the fourth period; or

sending the PMI₂ to the base station according to a second period;

sending the PMI₃ to the base station according to a third period; andsending the PMI₅ to the base station according to a fifth period, wherethe third period is less than the second period and the fifth period.

In a fifth possible implementation manner, with reference to the thirdpossible implementation manner, the sending a precoding matrix indicatorPMI to the base station specifically includes:

sending the PMI₁ to the base station according to a first frequencydomain granularity; and

sending the PMI₂ to the base station according to a second frequencydomain granularity, where the first frequency domain granularity isgreater than the second frequency domain granularity; or

sending the PMI₃ to the base station according to a third frequencydomain granularity; and

sending the PMI₄ to the base station according to a fourth frequencydomain granularity, where the third frequency domain granularity isgreater than the fourth frequency domain granularity; or

sending the PMI₂ to the base station according to a second frequencydomain granularity;

sending the PMI₃ to the base station according to a third frequencydomain granularity; and

sending the PMI₅ to the base station according to a fifth frequencydomain granularity, where the third frequency domain granularity is lessthan the second frequency domain granularity and the fifth frequencydomain granularity.

In a sixth possible implementation manner, with reference to the firstaspect or the first to fifth possible implementation manners, the blockmatrix X_(i)=[X_(i,1) X_(i,2)], where each column of the matrix X_(i,j)is selected from columns of a Householder matrix, a discrete Fouriertransform matrix, a Hadamard matrix, a rotated Hadamard matrix, or aprecoding matrix in an LTE R8 system 2-antenna or 4-antenna codebook orin an LTE R10 system 8-antenna codebook.

In a seventh possible implementation manner, with reference to the sixthpossible implementation manner, each column of the matrix X_(i,j), j=1,2is separately selected from columns of different Householder matrices,different discrete Fourier transform matrices, different Hadamardmatrices, different rotated Hadamard matrices, or different precodingmatrices in an LTE R8 system 2-antenna or 4-antenna codebook or in anLTE R10 system 8-antenna codebook.

In an eighth possible implementation manner, with reference to the firstaspect or the first to fifth possible implementation manners, the blockmatrix X_(i)=[X_(i,1) X_(i,2)], where the matrix X_(i,j) is a Kroneckerproduct of two matrices being A_(i,j) and B_(i,j), and j=1,2.

In a ninth possible implementation manner, with reference to the eighthpossible implementation manner, columns of the matrix X_(i,1) and thematrix X_(i,2) are column vectors of a Householder matrix, a DFT matrix,a Hadamard matrix, a rotated Hadamard matrix, or a precoding matrix inan LTE R8 system 2-antenna or 4-antenna codebook or in an LTE R10 system8-antenna codebook.

In a tenth possible implementation manner, with reference to the firstaspect or the first to ninth possible implementation manners, W₁ is anidentity matrix.

In an eleventh possible implementation manner, with reference to thefirst aspect or the first to tenth possible implementation manners, acolumn vector in the matrix W₂ has a structure y_(n)=γ⁻¹[e_(n) ^(T)e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) represents a selection vector;where in the vector, the n^(th) element is 1 and all other elements are0; θ_(n) is a phase shift; and γ is a positive constant.

According to a second aspect, an embodiment of the present inventionprovides a method for reporting channel state information, where themethod includes:

sending a reference signal to user equipment UE;

receiving a precoding matrix indicator PMI sent by the UE; and

determining a precoding matrix W in a codebook according to the PMI,where the precoding matrix W is a product of three matrices being W₁, Z,and W₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag{Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, andβ_(i,k)≥0.

In a first possible implementation manner, with reference to the secondaspect, the determining a precoding matrix W in a codebook according tothe PMI specifically includes:

determining the precoding matrix in a codebook subset according to thePMI, where the codebook subset is a subset predefined, or reported bythe user equipment, or notified by a base station.

In a second possible implementation manner, with reference to the firstpossible implementation manner, the codebook subsets share at least onesame matrix subset of the following matrix subsets: subsets of a matrixW₁, a matrix W₁Z, a matrix W₂, a matrix ZW₂, and a matrix Z.

In a third possible implementation manner, with reference to the secondaspect or the first and second possible implementation manners, thereceiving a precoding matrix indicator PMI sent by the UE specificallyincludes:

receiving a first precoding matrix indicator PMI₁ and a second precodingmatrix indicator PMI₂ that are sent by the UE, where the PMI₁ is used toindicate the matrix W₁Z, and the PMI₂ is used to indicate the matrix W₂;

or

receiving a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ that are sent by the UE, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;

or

receiving a second precoding matrix indicator PMI₂, a third precodingmatrix indicator PMI₃, and a fifth precoding matrix indicator PMI₅ thatare sent by the UE, where the PMI5 is used to indicate the matrix Z.

In a fourth possible implementation manner, with reference to the thirdpossible implementation manner, the receiving a precoding matrixindicator PMI sent by the UE specifically includes:

receiving, according to a first period, the PMI₁ sent by the UE; and

receiving, according to a second period, the PMI₂ sent by the UE, wherethe first period is greater than the second period; or

receiving, according to a third period, the PMI₃ sent by the UE; and

receiving, according to a fourth period, the PMI₄ sent by the UE, wherethe third period is greater than the fourth period; or

receiving, according to a second period, the PMI₂ sent by the UE;

receiving, according to a third period, the PMI₃ sent by the UE; and

receiving, according to a fifth period, the PMI₅ sent by the UE, wherethe third period is less than the second period and the fifth period.

In a fifth possible implementation manner, with reference to the thirdpossible implementation manner, the receiving a precoding matrixindicator PMI sent by the UE specifically includes:

receiving, according to a first frequency domain granularity, the PMI₁sent by the UE; and

receiving, according to a second frequency domain granularity, the PMI₂sent by the UE, where the first frequency domain granularity is greaterthan the second frequency domain granularity; or

receiving, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receiving, according to a fourth frequency domain granularity, the PMI₄sent by the UE, where the third frequency domain granularity is greaterthan the fourth frequency domain granularity; or

receiving, according to a second frequency domain granularity, the PMI₂sent by the UE;

receiving, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receiving, according to a fifth frequency domain granularity, the PMI₅sent by the UE, where the third frequency domain granularity is lessthan the second frequency domain granularity and the fifth frequencydomain granularity.

In a sixth possible implementation manner, with reference to the secondaspect or the first to fifth possible implementation manners, the blockmatrix X_(i)=[X_(i,1) X_(i,2)], where each column of the matrix X_(i,j)is selected from columns of a Householder matrix, a discrete Fouriertransform matrix, a Hadamard matrix, a rotated Hadamard matrix, or aprecoding matrix in an LTE R8 system 2-antenna or 4-antenna codebook orin an LTE R10 system 8-antenna codebook.

In a seventh possible implementation manner, with reference to the sixthpossible implementation manner, each column of the matrix X_(i,j), j=1,2is separately selected from columns of different Householder matrices,different discrete Fourier transform matrices, different Hadamardmatrices, different rotated Hadamard matrices, or different precodingmatrices in an LTE R8 system 2-antenna or 4-antenna codebook or in anLTE R10 system 8-antenna codebook.

In an eighth possible implementation manner, with reference to thesecond aspect or the first to fifth possible implementation manners, theblock matrix X_(i)=[X_(i,1) X_(i,2)], where the matrix X_(i,j) is aKronecker product of a matrix A_(i,j) and a matrix B_(i,j), and j=1,2.

In a ninth possible implementation manner, with reference to the eighthpossible implementation manner, columns of the matrix X_(i,1) and thematrix X_(i,2) are column vectors of a Householder matrix, a discreteFourier transform matrix, a Hadamard matrix, a rotated Hadamard matrix,or a precoding matrix in an LTE R8 system 2-antenna or 4-antennacodebook or in an LTE R0 system 8-antenna codebook.

In a tenth possible implementation manner, with reference to the secondaspect or the first to ninth possible implementation manners, W₁ is anidentity matrix.

In an eleventh possible implementation manner, with reference to thesecond aspect or the first to tenth possible implementation manners, acolumn vector in the matrix W₂ has a structure y_(n)=γ⁻¹[e_(n) ^(T)e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) represents a selection vector;where in the vector, the n^(th) element is 1 and all other elements are0; θ_(n), is a phase shift; and γ is a positive constant.

According to a third aspect, an embodiment of the present inventionprovides user equipment, where the user equipment includes: a receivingunit, a selection unit, and a sending unit, where

the receiving unit is configured to receive a reference signal sent by abase station;

the selection unit is configured to select, based on the referencesignal, a precoding matrix from a codebook, where a precoding matrix Wincluded in the codebook is a product of three matrices being W₁, Z, andW₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag{Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, andβ_(i,k)≥0; and

the sending unit is configured to send a precoding matrix indicator PMIto the base station, where the PMI corresponds to the selected precodingmatrix, and is used by the base station to obtain the selected precodingmatrix W according to the PMI.

In a first possible implementation manner, with reference to the thirdaspect, the selection unit is specifically configured to select, basedon the reference signal, the precoding matrix from a codebook subset,where the codebook subset is a subset predefined, or notified by thebase station, or reported by the user equipment.

In a second possible implementation manner, with reference to the firstpossible implementation manner, the codebook subsets share at least onesame matrix subset of the following matrix subsets: subsets of a matrixW₁, a matrix W₁Z, a matrix W₂, a matrix ZW₂, and a matrix Z.

In a third possible implementation manner, with reference to the thirdaspect or the first and second possible implementation manners, thesending unit is specifically configured to send a first precoding matrixindicator PMI, and a second precoding matrix indicator PMI₂ to the basestation, where the PMI₁ is used to indicate the matrix W₁Z, and the PMI₂is used to indicate the matrix W₂; or

send a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ to the base station, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;or

send a second precoding matrix indicator PMI₂, a third precoding matrixindicator PMI₃, and a fifth precoding matrix indicator PMI₅ to the basestation, where the PMI₅ is used to indicate the matrix Z.

In a fourth possible implementation manner, with reference to the thirdpossible implementation manner, the sending unit is specificallyconfigured to send the PMI₁ to the base station according to a firstperiod; and

send the PMI₂ to the base station according to a second period, wherethe first period is greater than the second period; or

send the PMI₃ to the base station according to a third period; and

send the PMI₄ to the base station according to a fourth period, wherethe third period is greater than the fourth period; or

send the PMI₂ to the base station according to a second period;

send the PMI₃ to the base station according to a third period; and

send the PMI₅ to the base station according to a fifth period, where thethird period is less than the second period and the fifth period.

In a fifth possible implementation manner, with reference to the thirdpossible implementation manner, the sending unit is specificallyconfigured to send the PMI₁ to the base station according to a firstfrequency domain granularity; and

send the PMI₂ to the base station according to a second frequency domaingranularity, where the first frequency domain granularity is greaterthan the second frequency domain granularity; or

send the PMI₃ to the base station according to a third frequency domaingranularity; and

send the PMI₄ to the base station according to a fourth frequency domaingranularity, where the third frequency domain granularity is greaterthan the fourth frequency domain granularity; or

send the PMI₂ to the base station according to a second frequency domaingranularity;

send the PMI₃ to the base station according to a third frequency domaingranularity; and

send the PMI to the base station according to a fifth frequency domaingranularity, where the third frequency domain granularity is less thanthe second frequency domain granularity and the fifth frequency domaingranularity.

In a sixth possible implementation manner, with reference to the thirdaspect or the first to fifth possible implementation manners, the blockmatrix X_(i)=[X_(i,1) X_(i,2)], where each column of the matrix X_(i,j)is selected from columns of a Householder matrix, a discrete Fouriertransform matrix, a Hadamard matrix, a rotated Hadamard matrix, or aprecoding matrix in an LTE R8 system 2-antenna or 4-antenna codebook orin an LTE R10 system 8-antenna codebook.

In a seventh possible implementation manner, with reference to the sixthpossible implementation manner, each column of the matrix X_(i,j), j=1,2is separately selected from columns of different Householder matrices,different discrete Fourier transform matrices, different Hadamardmatrices, different rotated Hadamard matrices, or different precodingmatrices in an LTE R8 system 2-antenna or 4-antenna codebook or in anLTE R10 system 8-antenna codebook.

In an eighth possible implementation manner, with reference to the thirdaspect or the first to fifth possible implementation manners, the blockmatrix X_(i)=[X_(i,1) X_(i,2)], where the matrix X_(i,j) is a Kroneckerproduct of two matrices being A_(i,j) and B_(i,j), and j=1,2.

In a ninth possible implementation manner, with reference to the eighthpossible implementation manner, columns of the matrix X_(i,1) and thematrix X_(i,2) are column vectors of a Householder matrix, a discreteFourier transform matrix, a Hadamard matrix, a rotated Hadamard matrix,or a precoding matrix in an LTE R8 system 2-antenna or 4-antennacodebook or in an LTE R system 8-antenna codebook.

In a tenth possible implementation manner, with reference to the thirdaspect or the first to ninth possible implementation manners, W₁ is anidentity matrix.

In an eleventh possible implementation manner, with reference to thethird aspect or the first to tenth possible implementation manners, acolumn vector in the matrix W₂ has a structure y_(n)=γ⁻¹[e_(n) ^(T)e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) represents a selection vector;where in the vector, the n^(th) element is 1 and all other elements are0; θ_(n), is a phase shift; and γ is a positive constant.

According to a fourth aspect, an embodiment of the present inventionprovides a base station, where the base station includes: a sendingunit, a receiving unit, and a determining unit, where

the sending unit is configured to send a reference signal to userequipment UE;

the receiving unit is configured to receive a precoding matrix indicatorPMI sent by the UE; and

the determining unit is configured to determine a precoding matrix W ina codebook according to the PMI, where the precoding matrix W is aproduct of three matrices being W₁, Z, and W₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag{Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, andβ_(i,k)≥0.

In a first possible implementation manner, with reference to the fourthaspect, the determining unit is specifically configured to:

determine the precoding matrix in a codebook subset according to thePMI, where the codebook subset is a subset predefined, or reported bythe user equipment, or notified by the base station.

In a second possible implementation manner, with reference to the firstpossible implementation manner, the codebook subsets share at least onesame matrix subset of the following matrix subsets: subsets of a matrixW₁, a matrix W₁Z, matrix W₂, a matrix ZW₂, and a matrix Z.

In a third possible implementation manner, with reference to the fourthaspect or the first and second possible implementation manners, thereceiving unit is specifically configured to:

receive a first precoding matrix indicator PMI₁ and a second precodingmatrix indicator PMI₂ that are sent by the UE, where the PMI₁ is used toindicate the matrix W₁Z, and the PMI₂ is used to indicate the matrix W₂;

or

receive a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ that are sent by the UE, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;

or

receive a second precoding matrix indicator PMI₂, a third precodingmatrix indicator PMI₃, and a fifth precoding matrix indicator PMI₅ thatare sent by the UE, where the PMI₅ is used to indicate the matrix Z.

In a fourth possible implementation manner, with reference to the thirdpossible implementation manner, the receiving unit is specificallyconfigured to:

receive, according to a first period, the PMI₁ sent by the UE; and

receive, according to a second period, the PMI₂ sent by the UE, wherethe first period is greater than the second period; or

receive, according to a third period, the PMI₃ sent by the UE; and

receive, according to a fourth period, the PMI₄ sent by the UE, wherethe third period is greater than the fourth period; or

receive, according to a second period, the PMI₂ sent by the UE;

receive, according to a third period, the PMI₃ sent by the UE; and

receive, according to a fifth period, the PMI₅ sent by the UE, where thethird period is less than the second period and the fifth period.

In a fifth possible implementation manner, with reference to the thirdpossible implementation manner, the receiving unit is specificallyconfigured to:

receive, according to a first frequency domain granularity, the PMI₁sent by the UE; and

receive, according to a second frequency domain granularity, the PMI₂sent by the UE, where the first frequency domain granularity is greaterthan the second frequency domain granularity; or

receive, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receive, according to a fourth frequency domain granularity, the PMI₄sent by the UE, where the third frequency domain granularity is greaterthan the fourth frequency domain granularity; or

receive, according to a second frequency domain granularity, the PMI₂sent by the UE;

receive, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receive, according to a fifth frequency domain granularity, the PMI₅sent by the UE, where the third frequency domain granularity is lessthan the second frequency domain granularity and the fifth frequencydomain granularity.

In a sixth possible implementation manner, with reference to the fourthaspect or the first to fifth possible implementation manners, the blockmatrix X_(i)=[X_(i,1) X_(i,2)], where each column of the matrix X_(i,j)is selected from columns of a Householder matrix, a discrete Fouriertransform matrix, a Hadamard matrix, a rotated Hadamard matrix, or aprecoding matrix in an LTE R8 system 2-antenna or 4-antenna codebook orin an LTE R1 system 8-antenna codebook.

In a seventh possible implementation manner, with reference to the sixthpossible implementation manner, each column of the matrix X_(i,j) isseparately selected from columns of different Householder matrices,different discrete Fourier transform matrices, different Hadamardmatrices, different rotated Hadamard matrices, or different precodingmatrices in an LTE R8 system 2-antenna or 4-antenna codebook or in anLTE R10 system 8-antenna codebook.

In an eighth possible implementation manner, with reference to thefourth aspect or the first to fifth possible implementation manners, theblock matrix X_(i)=[X_(i,1) X_(i,2)], where the matrix X_(i,j) is aKronecker product of two matrices being A_(i,j) and B_(i,j), and j=1,2.

In a ninth possible implementation manner, with reference to the eighthpossible implementation manner, columns of the matrix X_(i,1) and thematrix X_(i,2) are column vectors of a Householder matrix, a discreteFourier transform matrix, a Hadamard matrix, a rotated Hadamard matrix,or a precoding matrix in an LTE R8 system 2-antenna or 4-antennacodebook or in an LTE R system 8-antenna codebook.

In a tenth possible implementation manner, with reference to the fourthaspect or the first to ninth possible implementation manners, W₁ is anidentity matrix.

In an eleventh possible implementation manner, with reference to thefourth aspect or the first to tenth possible implementation manners, acolumn vector in the matrix W₂ has a structure y_(n)=γ⁻¹[e_(n) ^(T)e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) represents a selection vector;where in the vector, the n^(th) element is 1 and all other elements are0; θ_(n), is a phase shift; and γ is a positive constant.

The embodiments of the present invention provide a method for reportingchannel state information, user equipment, and a base station. Themethod includes: after receiving reference information sent by a basestation, selecting, by user equipment based on the referenceinformation, a precoding matrix from a codebook, where a precodingmatrix W included in the codebook is a product of three matrices beingW₁, Z, and W₂, where both W₁ and Z are block diagonal matrices,W₁=diag{X₁, . . . , X_(N) _(B) }, Z=diag{Z₁, . . . , Z_(N) _(B) }, eachof W₁ and Z includes at least one block matrix, that is, N_(B)≥1, andeach column of each block matrix Z_(i) in the matrix Z has the followingstructure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, andβ_(i,k)≥0; and sending a precoding matrix indicator PMI to the basestation according to the selected precoding matrix W, where the PMI isused by the base station to obtain the selected precoding matrix Waccording to the PMI. In the precoding matrix indicated in the channelstate information reported by the user equipment, a channelcharacteristic of a double-transmission condition in a micro cellnetwork environment and freedom in a perpendicular direction of anantenna are considered, which can improve communication performance ofthe micro cell network environment and the freedom in the perpendiculardirection of the antenna.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention or in the prior art more clearly, the following brieflyintroduces the accompanying drawings required for describing theembodiments or the prior art. Apparently, the accompanying drawings inthe following descriptions show merely some embodiments of the presentinvention, and a person of ordinary skill in the art may still deriveother drawings from these accompanying drawings without creativeefforts.

FIG. 1 is a schematic flowchart of a method for reporting channel stateinformation according to an embodiment of the present invention;

FIG. 2 is a schematic flowchart of another method for reporting channelstate information according to an embodiment of the present invention;

FIG. 3 is a schematic flowchart of still another method for reportingchannel state information according to an embodiment of the presentinvention;

FIG. 4 is a schematic diagram of interaction in a method for reportingchannel state information according to an embodiment of the presentinvention;

FIG. 5 is a schematic structural diagram of user equipment according toan embodiment of the present invention;

FIG. 6 is a schematic structural diagram of another user equipmentaccording to an embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a base station according toan embodiment of the present invention; and

FIG. 8 is a schematic structural diagram of another base stationaccording to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Various technologies described in this specification are applicable to aLong Term Evolution (LTE, Long Term Evolution) system. The userequipment may be a wireless terminal or a wired terminal. The wirelessterminal may refer to a device that provides a user with voice and/ordata connectivity, a handheld device with a radio connection function,or another processing device connected to a radio modem. The wirelessterminal may communicate with one or more core networks through a radioaccess network (for example, RAN, Radio Access Network). The wirelessterminal may be a mobile terminal, such as a mobile phone (also referredto as a “cellular” phone) and a computer with a mobile terminal, forexample, may be a portable, pocket-sized, handheld, computer built-in,or in-vehicle mobile apparatus, which exchanges voice and/or data withthe radio access network. For example, it may be a device such as apersonal communications service (PCS, Personal Communication Service)phone, a cordless telephone set, a Session Initiation Protocol (SIP)phone, a wireless local loop (WLL, Wireless Local Loop) station, or apersonal digital assistant (PDA, Personal Digital Assistant). Thewireless terminal may also be referred to as a system, a subscriber unit(Subscriber Unit), a subscriber station (Subscriber Station), a mobilestation (Mobile Station), a mobile station (Mobile), a remote station(Remote Station), an access point (Access Point), a remote terminal(Remote Terminal), an access terminal (Access Terminal), a user terminal(User terminal), a user agent (User agent), a user device (User Device),user equipment (User Equipment), or a relay (Relay), which is notlimited in the present invention.

In addition, the terms “system” and “network” may be usedinterchangeably in this specification. The term “and/or” in thisspecification describes only an association relationship for describingassociated objects and represents that three relationships may exist.For example, A and/or B may represent the following three cases: Only Aexists, both A and B exist, and only B exists. In addition, thecharacter “/” in this specification generally indicates an “or”relationship between the associated objects.

Embodiment 1

This embodiment of the present invention provides a method for reportingchannel state information. The method is executed by user equipment UE,and as shown in FIG. 1, the method includes:

Step 101: Receive a reference signal sent by a base station.

Specifically, the reference signal sent by the base station may includea channel state information reference signal (channel state informationReference Signal, CSI RS), or a demodulation reference signal(demodulation RS, DM RS), or a cell-specific reference signal(cell-specific RS, CRS). The user equipment UE may obtain a resourceconfiguration of the reference signal by receiving a notification of theeNB such as RRC (Radio Resource Control, Radio Resource Control)signaling or DCI (Downlink Control Information, downlink controlinformation), or on the basis of a cell identity ID; and obtain thereference signal in a corresponding resource or subframe.

Step 102: Select, based on the reference signal, a precoding matrix froma codebook, where a precoding matrix W included in the codebook is aproduct of three matrices being W₁, Z, and W₂, that is,

W=W ₁ ZW ₂  (1)

where both W₁ and Z are block diagonal matrices, that is:

W ₁=diag{X ₁ , . . . ,X _(N) _(B) }  (2)

Z=diag{Z ₁ , . . . ,Z _(N) _(B) }  (3)

and meet the following condition:

W ₁ Z=diag{X ₁ ,Z ₁ , . . . ,X _(N) _(B) Z _(N) _(B) }  (4)

each of W₁ and Z includes at least one block matrix, that is, a blockmatrix quantity N_(B)≥1, and each column of each block matrix Z_(i) inthe matrix Z has the following structure:

$\begin{matrix}{z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}} & (5)\end{matrix}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i), that is, 2n_(i) is a column quantity of theblock matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, β_(i,k)≥0; andX_(i) corresponds to Z_(i).

In the structure (5), for the precoding matrix, two column vectors (orreferred to as beams) can be separately selected from each block matrixX_(i) by using two e_(i,k) in z_(i,k); and phase alignment and weightingare performed on the two column vectors (or beams) by using α_(i,k) andβ_(i,k)e^(jθ) ^(i,k) , where the two column vectors selected from X_(i)may separately point to two major multipath transmission directions.

In analysis from the perspective of physical meaning, the block diagonalmatrix W₁ is a beam group formed by the block matrices X_(i) thatinclude different beams (or column vectors), and correspondingly, eachcolumn of each block matrix Z_(i) included in the matrix Z is used tocombine (including phase alignment and weighting) two beams in the blockmatrix X_(i), where directions of the two beams may separately point totwo major multipath transmission directions. Therefore, for each columnof an obtained matrix X_(i)Z_(i), interference between two majormultipath transmission directions can be converted into a wanted signalby using the foregoing structure, thereby significantly improvingtransmit power corresponding to each column of X_(i)Z_(i).

The parameters α_(i,k) and β_(i,k) may be equal, and in this case,equal-power combining gains of two beams are obtained. One of theparameters α_(i,k) and β_(i,k) may be 0, and in this case, selectivecombining gains of two beams are obtained. The parameters α_(i,k) andβ_(i,k) may also be other quantized values, for example, a value ofβ_(i,k)e^(jθ) ^(i,k) may be selected from a constellation diagram ofmodulation such as 16QAM or 64QAM, and in this case, maximum ratiocombining gains of two beams are obtained.

The matrix W₂ is used to select one or more column vectors in the matrixW₁Z and perform weighting combination to form the matrix W. By using thematrix W₂, the precoding matrix W can further adapt to a sub-band or ashort-term characteristic of a channel, and one-layer or multi-layertransmission is formed, thereby improving a transmission rate.

Specifically, the block matrix X_(i) in the matrix W₁ may have thefollowing structure:

X _(i)=[X _(i,1) ,X _(i,2)], 1≤i≤N _(B)  (6)

where, each column of the matrix X_(i,j) may be selected from columns ofa Householder (Householder) matrix H, where the matrix H is:

H∈{I−2u _(n) u _(n) ^(H) /u _(n) ^(H) u _(n)}  (7)

For example, the vector u_(n) may be a vector used in an LTE R84-antenna codebook, and is shown in the following table:

   u₀ = [1 −1 −1 −1]^(T)  u₁ = [1 −j 1 j ]^(T)  u₂ = [1 1 −1 1]^(T)  u₃= [1 j 1 −j]^(T)  u₄ = [1 (−1 − j)/{square root over (2)} −j (1 −j)/{square root over (2)}]^(T)  u₅ = [1 (1 − j)/{square root over (2)} j(−1 − j)/{square root over (2)}]^(T)  u₆ = [1 (1 + j)/{square root over(2)} −j (−1 + j/{square root over (2)}]^(T)  u₇ = [1 (−1 + j)/{squareroot over (2)} j (1 + j)/{square root over (2)}]^(T)  u₈ = [1 −1 11]^(T)  u₉ = [1 −j −1 −j]^(T) u₁₀ = [1 1 1 −1]^(T) u₁₁ = [1 j −1 j]^(T)u₁₂ = [1 −1 −1 1]^(T) u₁₃ = [1 −1 1 −1]^(T) u₁₄ = [1 1 −1 −1]^(T) u₁₅ =[1 1 1 1]^(T)

Each column in the two matrices X_(i,j), j=1,2 may be from a column setof a same Householder matrix H, or may be separately from column sets ofdifferent Householder matrices H. In the former case, columns inX_(i,j), j=1,2 are orthogonal to each other, and it is suitable formultipath transmission directions that are orthogonal to each other. Inthe latter case, columns in X_(i,j) j=1,2 may be close to each other,and it is suitable for multipath transmission directions that are notorthogonal to each other.

Each column of the matrix X_(i,j) in formula (6) may also be selectedfrom columns of a discrete Fourier transform (Discrete FourierTransform, DFT) matrix F where the matrix F is:

$\begin{matrix}{F \in \{ {{F_{g} = \lbrack e^{j\frac{2\; \pi \; m}{N}{({n + {g/G}})}} \rbrack_{N \times N}},{g = 0},1,{{\ldots \mspace{14mu} G} - 1}} \}} & (8)\end{matrix}$

where

$\lbrack e^{j\frac{2\; \pi \; m}{N}{({n + \frac{g}{G}})}} \rbrack_{N \times N}$

represents that an element in the (m+1)^(th) row and the (n+1)^(th)column is an N×N matrix of

$e^{j\frac{2\; \pi \; m}{N}{({n + {g/G}})}},$

where

m,n=0,1 . . . , N−1; j represents a unit pure imaginary number, that is,j=√{square root over (−1)}; G is a positive integer; and g/G is a phaseshift parameter. Multiple different DFT matrices may be obtained byselecting G and g. Columns of the two matrices X_(i,j), j=1,2 may befrom a same DFT matrix F, or may be from different DFT matrices F. Inthe former case, columns in X_(i,j), j=1,2 are orthogonal to each other,and it is suitable for multipath transmission directions that areorthogonal to each other. In the latter case, columns in X_(i,j), j=1,2may be close to each other, and it is suitable for multipathtransmission directions that are not orthogonal to each other.

Each column of the matrix X_(i,j) in formula (6) may also be selectedfrom columns of the following Hadamard (Hadamard) matrix or rotatedHadamard matrix:

diag{1,e ^(jmπ/N) ,e ^(jmπ/N) ,e ^(j3m/N) }H _(n)  (9)

where N is a positive integer, m=0, . . . , N−1, H_(n) is an n-orderHadamard matrix, and j represents a unit pure imaginary number, that is,j=√{square root over (−1)}. When m=0, a matrix shown in (10) is ann-order Hadamard matrix H_(n). For example, H₄ is:

$\begin{matrix}{H_{4} = \begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}} & (10)\end{matrix}$

Columns in the two matrices X_(i,j) j=1,2 may be from a same Hadamardmatrix or rotated Hadamard matrix, or may be from different Hadamardmatrices or rotated Hadamard matrices. In the former case, columns inX_(i,j), j=1,2 are orthogonal to each other, and it is suitable formultipath transmission directions that are orthogonal to each other. Inthe latter case, columns in X_(i,j), j=1,2 may be close to each other,and it is suitable for multipath transmission directions that are notorthogonal to each other.

Each column of the matrix X_(i,j) in formula (6) may also be selectedfrom columns of a precoding matrix in an LTE R8 system 2-antenna or4-antenna codebook or in an LTE R10 system 8-antenna codebook. Columnsof the two matrices X_(i,j), j=1,2 may be from a same precoding matrix,or may be from different precoding matrices. In the former case, columnsin X_(i,j), j=1,2 are orthogonal to each other, and it is suitable formultipath transmission directions that are orthogonal to each other. Inthe latter case, columns in X_(i,j), j=1,2 may be close to each other,and it is suitable for multipath transmission directions that are notorthogonal to each other.

The matrix X_(i,j) in formula (6) may also have the following structure:

X _(i,j) =A _(i,j) ⊗B _(i,j), 1≤i≤N _(B) , j=1,2  (11)

That is, the block matrix X_(i,j) is a Kronecker (kronecker) product ofa matrix A_(i,j) and a matrix B_(i,j), where j=1,2.

Further, each column of the matrix A_(i,j) or the matrix B_(i,j) informula (11) may be a column vector of the Householder matrix shown in(7), or the DFT matrix shown in (8), or the Hadamard matrix or therotated Hadamard matrix shown in (9) or (10), or the precoding matrix inthe LTE R8 system 2-antenna or 4-antenna codebook or in the LTE R10system 8-antenna codebook. In addition, other forms may also be used forthe matrix A_(i,j) or the matrix B_(i,j), which are not described indetail herein.

For the matrix A_(i,j) or the matrix B_(i,j) in the structure (11),beamforming and precoding may be separately performed in a horizontaldirection and a perpendicular direction of an AAS base station.Therefore, the precoding matrix W can adapt to an antenna configurationof the AAS base station, thereby fully using freedom in horizontal andperpendicular directions of an antenna of the AAS base station.

Columns in the two matrices being A_(i,j) and B_(i,j), j=1,2 may be froma same precoding matrix in formula (7) to formula (10) or in the LTE R8system 2-antenna or 4-antenna codebook or in the LTE R10 system8-antenna codebook, or may be from different precoding matrices. In theformer case, columns in X_(i,j), j=1,2 are orthogonal to each other, andit is suitable for multipath transmission directions that are orthogonalto each other. In the latter case, columns in X_(i,j), j=1,2 may beclose to each other, and it is suitable for multipath transmissiondirections that are not orthogonal to each other.

Further, the block matrices X_(i) in formula (6) may be equal to eachother, where 1≤i≤N_(B); in this way, relevance between channels can befully used, and feedback overheads can be further reduced.

Specifically, the block matrix X_(i) in the matrix W₁ may also be anidentity matrix, that is, W₁ is an identity matrix; and in this case,W₁Z=Z. In this case, the structure shown in (5) helps select two antennaports by directly using two e_(i,k) in z_(i,k), and helps perform phasealignment and weighting on the two antenna ports by using

α_(i, k)e^(j θ_(i, k)),

where the two selected antenna ports may separately align with two majormultipath transmission directions. An actually deployed antenna port maycorrespond to a virtual antenna, where each virtual antenna is obtainedby performing weighting combination on multiple physical antennas, andvirtual antennas may have different beam directions; therefore, in theforegoing precoding structure, different beam directions of the antennaports can be fully used, and interference between two major multipathtransmission directions can be directly converted into a wanted signal,thereby significantly improving a system transmission rate.

Specifically, the phase θ_(i,k) in the structure (5) may be selectedfrom the following values:

$\begin{matrix}{\theta_{i,k} \in \{ {0,\frac{2\pi}{N},\ldots \mspace{14mu},\ \frac{( {N - 1} )2\pi}{N}} \}} & (12)\end{matrix}$

where N is a positive integer, for example, N is 2 to the power of n,where n is a positive integer.

Further, the foregoing block matrices Z_(i) may be equal to each other,where 1≤i≤N_(B); in this way, relevance between channels can be fullyused, and feedback overheads can be further reduced.

The matrix W₂ is used to select or perform weighting combination on acolumn vector in the matrix W₁Z to form the matrix W.

Specifically, a column vector in the matrix W₂ has a structure:y_(n)=γ⁻¹[e_(n) ^(T) e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) representsa selection vector, where in the vector, the n^(th) element is 1 and allother elements are 0; θ_(n) is a phase shift; and β is a positiveconstant.

An example in which a block matrix quantity N_(B)=2, and two blockmatrices X₁Z and X₂Z₂ in W₁Z separately have 4 columns is used, and thematrix W₂ may be.

$\begin{matrix}{\mspace{20mu} {W_{2} \in \{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\ \begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \}}} & (13) \\{\mspace{20mu} {{Y \in \{ {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{4}} \}}\mspace{20mu} {or}}} & (14) \\{\mspace{20mu} {W_{2} \in \{ {{\frac{1}{\sqrt{2}}\ \begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \}}} & (15) \\{( {Y_{1},Y_{2}} ) \in \{ {( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{1}} ),( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{2}} ),( {{\overset{\sim}{e}}_{3},{\overset{\sim}{e}}_{3}} ),( {{\overset{\sim}{e}}_{4},{\overset{\sim}{e}}_{4}} ),( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{2}} ),( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{3}} ),( {{\overset{\sim}{e}}_{1},{\overset{\sim}{e}}_{4}} ),( {{\overset{\sim}{e}}_{2},{\overset{\sim}{e}}_{4}} )} \}} & (16)\end{matrix}$

where {tilde over (e)}_(n), n=1,2,3,4 represents a 4×1 selection vector,where in the vector, the n^(th) element is 1 and all other elements are0.

An example in which a block matrix quantity N_(B)=2, and two blockmatrices X₁Z₁ and X₂Z₂ in X₁Z separately have 8 columns is used, and thematrix W₂ may be:

$\begin{matrix}{\mspace{20mu} {W_{2} \in \{ {{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\Y\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{jY}\end{bmatrix}},{\frac{1}{\sqrt{2}}\ \begin{bmatrix}Y \\{- Y}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y \\{- {jY}}\end{bmatrix}}} \}}} & (17) \\{\mspace{20mu} {{Y \in \{ {e_{1},e_{2},e_{3},e_{4},e_{5},e_{6},e_{7},e_{8}} \}}\mspace{20mu} {or}}} & (18) \\{\mspace{20mu} {W_{2} \in \{ {{\frac{1}{\sqrt{2}}\ \begin{bmatrix}Y_{1} & Y_{2} \\Y_{1} & {- Y_{2}}\end{bmatrix}},{\frac{1}{\sqrt{2}}\begin{bmatrix}Y_{1} & Y_{2} \\{jY}_{1} & {- {jY}_{2}}\end{bmatrix}}} \}}} & (19) \\{( {Y_{1},Y_{2}} ) \in \{ {( {e_{1},e_{1}} ),( {e_{2},e_{2}} ),( {e_{3},e_{3}} ),( {e_{4},e_{4}} ),( {e_{1},e_{2}} ),( {e_{2},e_{3}} ),( {e_{1},e_{4}} ),( {e_{2},e_{4}} )} \}} & (20)\end{matrix}$

where e_(n), n=1,2, . . . , 8 represents an 8×1 selection vector, wherein the vector, the n^(th) element is 1 and all other elements are 0.

Specifically, the selecting, based on the reference signal, a precodingmatrix from a codebook may include:

obtaining, by the user equipment UE based on the reference signal,channel estimation, and selecting the precoding matrix from the codebookaccording to the channel estimation and based on a predefined rule suchas a rule of maximizing a channel capacity or a throughput, whereselection, based on a predefined rule, of a precoding matrix is theprior art, and is not described in detail herein.

Step 103: Send a precoding matrix indicator PMI to the base stationaccording to the selected precoding matrix W, where the PMI is used bythe base station to obtain the selected precoding matrix W according tothe PMI.

Specifically, the precoding matrix W is included in a precoding matrixset or a codebook, and the PMI is used to indicate the precoding matrixW selected from the precoding matrix set or the codebook.

Specifically, the sending a precoding matrix indicator PMI to the basestation includes: sending the precoding matrix indicator PMI to the basestation, where the PMI may only include a specific value, and in thiscase, the PMI directly indicates the precoding matrix W. For example,there are a total of 16 different precoding matrices, and PMI=0, . . . ,15 may be used to respectively indicate precoding matrices W marked as0, 1, . . . , 15.

Specifically, the sending a precoding matrix indicator PMI to the basestation may also include: sending precoding matrix indicators PMI₁ andPMI₂ to the base station, where the PMI₁ and the PMI₂ are respectivelyused to indicate the matrix W₁Z and the matrix W₂ in formula (1), and inthis case, the matrix W₁Z and the matrix W₂ are respectively indicatedby the PMI₁ and the PMI₂ in the codebook;

or

the sending a precoding matrix indicator PMI to the base station mayalso include: sending a third precoding matrix indicator PMI₃ and afourth precoding matrix indicator PMI₄ to the base station, where thePMI₃ is used to indicate the matrix W₁, and the PMI₄ is used to indicatethe matrix ZW₂;

or

sending a second precoding matrix indicator PMI₂, a third precodingmatrix indicator PMI₃, and a fifth precoding matrix indicator PMI₅ tothe base station, where the PMI₅ is used to indicate the matrix Z.

Further, the precoding matrix indicators PMI₁ and PMI₂, or PMI₃ andPMI₄, or PMI₂, PMI₃, and PMI₅ have different time domains or frequencydomain granularities. Specifically, the sending a precoding matrixindicator PMI to the base station specifically includes:

sending the PMI₁ to the base station according to a first period; and

sending the PMI₂ to the base station according to a second period, wherethe first period is greater than the second period; or

sending the PMI₃ to the base station according to a third period; and

sending the PMI₄ to the base station according to a fourth period, wherethe third period is greater than the fourth period; or

sending the PMI₂ to the base station according to a second period;

sending the PMI₃ to the base station according to a third period; and

sending the PMI₅ to the base station according to a fifth period, wherethe third period is less than the second period and the fifth period;or, sending the PMI₁ to the base station according to a first frequencydomain granularity; and

sending the PMI₂ to the base station according to a second frequencydomain granularity, where the first frequency domain granularity isgreater than the second frequency domain granularity, for example,sending a wideband PMI₁ and a sub-band PMI₂ to the base station; or

sending the PMI₃ to the base station according to a third frequencydomain granularity; and

sending the PMI₄ to the base station according to a fourth frequencydomain granularity, where the third frequency domain granularity isgreater than the fourth frequency domain granularity, for example,sending a wideband PMI₃ and a sub-band PMI₄ to the base station; or

sending the PMI₂ to the base station according to a second frequencydomain granularity;

sending the PMI₃ to the base station according to a third frequencydomain granularity; and

sending the PMI₅ to the base station according to a fifth frequencydomain granularity, where the third frequency domain granularity is lessthan the second frequency domain granularity and the fifth frequencydomain granularity, for example, sending a wideband PMI₂, a widebandPMI₅, and a sub-band PMI₃ to the base station.

It should be noted that, the sizes of the foregoing wideband andsub-band may vary with the size of a system bandwidth. For example, in a10 MHz LTE system that includes 50 physical resource blocks (ResourceBlock, RB), the wideband may include 50 RBs, and the size of thesub-band may be 6 consecutive RBs; and in a 5 MHz LTE system, thewideband may include 25 RBs, and the size of the sub-band may be 3consecutive RBs.

For the foregoing different time domains, or frequency domaingranularities, or reporting periods, feedback overheads can be furtherreduced by using time or frequency domain relevance between channels.

Specifically, the sending a precoding matrix indicator PMI to the basestation may also include: sending a precoding matrix indicator PMI1_(i),where 1≤i≤N_(B), and the PMI₂ to the base station; PMI1_(i), where1≤i≤N_(B), and the PMI₂ are respectively used to indicate the matrixX₁Z₁, where 1≤i≤N_(B), and the matrix W₂;

or sending a precoding matrix indicator PMI3_(i), where 1≤i≤N_(B), andthe PMI₄ to the base station; PMI3_(i), where 1≤i≤N_(B), is used toindicate X_(i), and the PMI₄ is used to indicate the matrix ZW₂;

or sending a precoding matrix indicator PMI3_(i), where 1≤i≤N_(B), thePMI₂, and the PMI₅ to the base station, where the PMI₅ is used toindicate the matrix Z.

Specifically, the sending a precoding matrix indicator PMI to the basestation may also include: sending a precoding matrix indicator PMI5_(i),where 1≤i≤N_(B)/2, and the PMI₂ to the base station; PMI5_(i), where1≤i≤N_(B)/2, and the PMI₂ are respectively used to indicate the matrixX_(2i−1)Z_(2i−1)=X_(2i)Z_(2i), where 1≤i≤N_(B)/2, and a matrix W₂; andin this case, X_(2i−1)Z_(2i−1)=X_(2i)Z_(2i) and the two matrices appearin pairs.

Specifically, the sending a precoding matrix indicator PMI to the basestation may be: sending, by the UE, the precoding matrix indicator PMIto the base station through a physical uplink control channel (PhysicalUplink Control Channel, PUCCH) or a physical uplink shared channel(Physical Uplink Shared Channel, PUSCH).

Further, the sending a precoding matrix indicator PMI to the basestation may be: separately sending, by the UE to the base station byusing different subframes or in different periods, the PMI₁ and thePMI₂, or the PMI₃ and the PMI₄, or the PMI₂, the PMI₃, and the PMI₅, orthe PMI1_(i), where 1≤i≤N_(B), and the PMI₂, or the PMI3,_(i) and thePMI₄, or the PMI3_(i), where 1≤i≤N_(B), the PMI₂, and the PMI₅, or thePMI5_(i), where 1≤i≤N_(B)/2, and the PMI₂.

Further, the sending a precoding matrix indicator PMI to the basestation may also be: separately sending, by the UE to the base stationaccording to different sub-bands or sub-band widths in a frequencydomain, the PMI₁ and the PMI₂, or the PMI₃ and the PMI₄, or the PMI₂,the PMI₃, and the PMI₅, or the PMI₁, where 1≤i≤N_(B), and the PMI₂, orthe PMI₃, and the PMI₄, or the PMI₃, where 1≤i≤N_(B), the PMI₂, and thePMI₅, or the PMI5_(i), where 1≤i≤N_(B)/2, and the PMI₂.

In addition, multiple block matrices X_(i) may separately correspond toantenna groups of different polarizations or different locations;therefore, the precoding matrix can match multiple antenna deploymentsor configurations. The foregoing codebook structure can significantlyimprove performance of MIMO, especially MU-MIMO.

In addition, one or more PMIs are fed back based on a subset, toindicate the precoding matrix; therefore, time/frequency domain/spacerelevance between channels is fully used, thereby significantly reducingfeedback overheads.

Further, as shown in FIG. 2, after the step 201 of receiving a referencesignal sent by a base station, the selecting, based on the referencesignal, a precoding matrix from a codebook is specifically:

202: Select, based on the reference signal, the precoding matrix from acodebook subset.

The codebook subset may be a predefined codebook subset; or may be acodebook subset as follows: the codebook subset is reported by the UE tothe base station eNB, notified by the base station eNB based on a reportof the UE, and then told by the base station to the UE; or may be acodebook subset that is determined and reported by the UE, for example,a recently reported codebook subset.

Further, the codebook subset and another codebook subset share at leastone same matrix subset of the following matrix subsets: subsets of amatrix W₁, a matrix W₁Z, a matrix W₂, a matrix ZW₂, and a matrix Z.

As described above, the precoding matrix is selected based on thecodebook subset, which can further reduce feedback overheads andimplementation complexity.

Further, the codebook subsets share a same subset of the matrix W₁, orthe matrix W₁Z, or the matrix W₂, or the matrix ZW₂, or the matrix Z,and therefore, the codebook subsets overlap with each other, which canovercome an edge effect of quantization of channel state information.

Further, in the precoding matrix, the block matrices X_(i) of the blockdiagonal matrix W₁ may be unequal, or may be equal. If the blockdiagonal matrix W₁ has multiple equal block matrices, for example, equalblock matrices may appear in pairs, feedback overheads can be furtherreduced.

It should be noted that, the three matrices W₁, Z, and W₂ included inthe precoding matrix W that is selected, based on the reference signal,from the codebook may further be multiplied by a scale factor, so as toimplement power normalization or power balancing. In addition, apartfrom the precoding matrix having the foregoing structure, the codebookmay further include other precoding matrices, so as to meet requirementsof other scenarios, which is not limited herein.

This embodiment of the present invention provides the method forreporting channel state information. The method includes: afterreceiving reference information sent by a base station, selecting, byuser equipment based on the reference information, a precoding matrixfrom a codebook, where a precoding matrix W included in the codebook isa product of three matrices being W₁, Z, and W₂, where both W₁ and Z areblock diagonal matrices, W=diag{X₁, . . . , X_(N) _(B) }, Z=diag{Z₁ . .. , Z_(N) _(B) }, each of W₁ and Z includes at least one block matrix,that is, N_(B)≥1, and each column of each block matrix Z_(i) in thematrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, andβ_(i,k)≥0; and sending a precoding matrix indicator PMI to the basestation according to the selected precoding matrix W, where the PMI isused by the base station to obtain the selected precoding matrix Waccording to the PMI. In the precoding matrix indicated in the channelstate information reported by the user equipment, a channelcharacteristic of a double-transmission condition in a micro cellnetwork environment and freedom in a perpendicular direction of anantenna are considered, that is, each column of each block matrix Z_(i)in the matrix Z has a structure:

$z_{i,k} = {{( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}.}$

For the precoding matrix, two column vectors (or referred to as beams)can be separately selected from each block matrix X_(i) by using thestructure of the matrix Z; and phase alignment and weighting areperformed on the two column vectors (or beams), where the two columnvectors selected from X_(i) may separately point to two major multipathtransmission directions. Therefore, by using the foregoing structure,for each column of an obtained matrix X_(i)Z_(i), interference betweentwo major multipath transmission directions can be converted into awanted signal, and combining gains are obtained, thereby improvingsystem transmission reliability and a system transmission throughput.

Embodiment 2

This embodiment of the present invention further provides a method forreporting channel state information. The method is executed by a basestation, and as shown in FIG. 3, the method includes:

301: Send a reference signal to user equipment UE.

302: Receive a precoding matrix indicator PMI sent by the UE.

303: Determine a precoding matrix W in a codebook according to the PMI,where the precoding matrix W is a product of three matrices being W₁, Z,and W₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag {Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, β_(i,k)≥0;and X_(i) corresponds to Z_(i).

It should be noted that, apart from the precoding matrix having theforegoing structure, the codebook may further include other precodingmatrices, so as to meet requirements of other scenarios, which is notlimited herein.

In this embodiment of the present invention, user equipment determinesand sends a precoding matrix indicator PMI, where the PMI indicates aprecoding matrix, and the precoding matrix has a structure: W=W₁ZW₂,where both W₁ and Z are block diagonal matrices, and each column of eachblock matrix Z_(i) in the matrix Z has a structure:

$z_{i,k} = {{( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}.}$

For the precoding matrix, two column vectors (or referred to as beams)can be separately selected from each block matrix X_(i) by using thestructure of the matrix Z; and phase alignment and weighting areperformed on the two column vectors (or beams), where the two columnvectors selected from X_(i) may separately point to two major multipathtransmission directions. Therefore, by using the foregoing structure,for each column of an obtained matrix X_(i)Z_(i), interference betweentwo major multipath transmission directions can be converted into awanted signal, and combining gains are obtained, thereby improvingsystem transmission reliability and a system transmission throughput.

Embodiment 3

Based on the methods for reporting channel state information provided inthe foregoing embodiments, the following describes in detail interactionbetween devices for implementing a method for reporting channel stateinformation provided in this embodiment of the present invention, and asshown in FIG. 4, the method includes:

401: A base station sends a reference signal to user equipment UE.

402: The user equipment receives the reference signal sent by the basestation.

403: The user equipment selects, based on the reference signal, aprecoding matrix from a codebook, where a precoding matrix W included inthe codebook is a product of three matrices being W₁, Z, and W₂, thatis, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag {Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, β_(i,k)≥0;and X_(i) corresponds to Z_(i).

404: The user equipment sends a precoding matrix indicator PMI to thebase station, where the PMI corresponds to the selected precodingmatrix, and is used by the base station to obtain the selected precodingmatrix W according to the PMI.

405: The base station receives the precoding matrix indicator PMI sentby the UE.

406: Determine the precoding matrix W in the codebook according to thePMI.

In this embodiment of the present invention, user equipment determinesand sends a precoding matrix indicator PMI, where the PMI indicates aprecoding matrix, and the precoding matrix has a structure: W=W₁ZW₂,where both W₁ and Z are block diagonal matrices, and each column of eachblock matrix Z_(i) in the matrix Z has a structure:

$z_{i,k} = {{( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}.}$

For the precoding matrix, two column vectors (or referred to as beams)can be separately selected from each block matrix X_(i) by using theforegoing structure; and phase alignment and weighting are performed onthe two column vectors (or beams), where the two column vectors selectedfrom X_(i) may separately point to two major multipath transmissiondirections. Therefore, by using the foregoing structure, for each columnof an obtained matrix X_(i)Z_(i), interference between two majormultipath transmission directions can be converted into a wanted signal,and combining gains are obtained, thereby improving system transmissionreliability and a system transmission throughput.

Embodiment 4

This embodiment of the present invention provides user equipment. Asshown in FIG. 5, the user equipment includes: a receiving unit 51, aselection unit 52, and a sending unit 53.

The receiving unit 51 is configured to receive a reference signal sentby a base station.

The selection unit 52 is configured to select, based on the referencesignal, a precoding matrix from a codebook, where a precoding matrix Wincluded in the codebook is a product of three matrices being W₁, Z, andW₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag{Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, β_(i,k)≥0;and X_(i) corresponds to Z_(i).

The sending unit 53 is configured to send a precoding matrix indicatorPMI to the base station, where the PMI corresponds to the selectedprecoding matrix, and is used by the base station to obtain the selectedprecoding matrix W according to the PMI.

Optionally, the selection unit 52 is specifically configured to select,based on the reference signal, the precoding matrix from a codebooksubset, where the codebook subset is a subset predefined, or notified bythe base station, or reported by the user equipment.

Preferably, the codebook subsets share at least one same matrix subsetof the following matrix subsets: subsets of a matrix W₁, a matrix W₁Z, amatrix W₂, a matrix ZW₂, and a matrix Z.

Optionally, the sending unit 53 may be specifically configured to send afirst precoding matrix indicator PMI₁ and a second precoding matrixindicator PMI₂ to the base station, where the PMI₁ is used to indicatethe matrix W₁Z, and the PMI₂ is used to indicate the matrix W₂; or

send a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ to the base station, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;or

send a second precoding matrix indicator PMI₂, a third precoding matrixindicator PMI₃, and a fifth precoding matrix indicator PMI₅ to the basestation, where the PMI₅ is used to indicate the matrix Z.

Optionally, the sending unit 53 may be specifically configured to sendthe PMI₁ to the base station according to a first period; and

send the PMI₂ to the base station according to a second period, wherethe first period is greater than the second period; or

send the PMI₃ to the base station according to a third period; and

send the PMI₄ to the base station according to a fourth period, wherethe third period is greater than the fourth period; or

send the PMI₂ to the base station according to a second period;

send the PMI₃ to the base station according to a third period; and

send the PMI₅ to the base station according to a fifth period, where thethird period is less than the second period and the fifth period.

The sending unit 53 may further be specifically configured to send thePMI₁ to the base station according to a first frequency domaingranularity; and

send the PMI₂ to the base station according to a second frequency domaingranularity, where the first frequency domain granularity is greaterthan the second frequency domain granularity, for example, send awideband PMI₁ and a sub-band PMI₂ to the base station; or

send the PMI₃ to the base station according to a third frequency domaingranularity; and

send the PMI₄ to the base station according to a fourth frequency domaingranularity, where the third frequency domain granularity is greaterthan the fourth frequency domain granularity, for example, send awideband PMI₃ and a sub-band PMI₄ to the base station; or

send the PMI₂ to the base station according to a second frequency domaingranularity;

send the PMI₃ to the base station according to a third frequency domaingranularity; and

send the PMI₅ to the base station according to a fifth frequency domaingranularity, where the third frequency domain granularity is less thanthe second frequency domain granularity and the fifth frequency domaingranularity, for example, send a wideband PMI₂, a wideband PMI₅, and asub-band PMI₃ to the base station.

It should be noted that, the sizes of the foregoing wideband andsub-band may vary with the size of a system bandwidth. For example, in a10 MHz LTE system, the wideband may include 50 physical resource blocksRBs, and the size of the sub-band may be 6 consecutive RBs; and in a 5MHz LTE system, the wideband may include 25 RBs, and the size of thesub-band may be 3 consecutive RBs.

Optionally, the block matrix X_(i)=[X_(i,1) X_(i,2)], where each columnof the matrix X_(i,j) is selected from columns of a Householder matrix,a discrete Fourier transform matrix, a Hadamard matrix, a rotatedHadamard matrix, or a precoding matrix in an LTE R8 system 2-antenna or4-antenna codebook or in an LTE R10 system 8-antenna codebook.

Further, each column of the matrix X_(i,j), j=1,2 is separately selectedfrom columns of different Householder matrices, different discreteFourier transform matrices, different Hadamard matrices, differentrotated Hadamard matrices, or different precoding matrices in an LTE R8system 2-antenna or 4-antenna codebook or in an LTE R10 system 8-antennacodebook.

Optionally, the block matrix X_(i)=[X_(i,1) X_(i,2)], where the matrixX_(i,j) is a Kronecker product of two matrices being A_(i,j) andB_(i,j), and j=1,2.

Further, columns of the matrix X_(i,1) and the matrix X_(i,2) are columnvectors of a Householder matrix, a discrete Fourier transform matrix, aHadamard matrix, a rotated Hadamard matrix, or a precoding matrix in anLTE R8 system 2-antenna or 4-antenna codebook or in an LTE R10 system8-antenna codebook.

Optionally, W₁ is an identity matrix.

Optionally, a column vector in the matrix W₂ has a structure:y_(n)=γ⁻¹[e_(n) ^(T) e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) representsa selection vector, where in the vector, the n^(th) element is 1 and allother elements are 0; θ_(n) is a phase shift; and γ is a positiveconstant.

This embodiment of the present invention further provides userequipment. As shown in FIG. 6, the user equipment includes: atransceiver 601, a memory 602, and a processor 603. Certainly, the userequipment may further include common-purpose components such as anantenna and an input/output apparatus, which is not limited herein inthis embodiment of the present invention.

The memory 602 stores a set of program code, and the processor 603 isconfigured to invoke the program code stored in the memory 602, toperform the following operations: receiving, by using the transceiver601, a reference signal sent by a base station; selecting, based on thereference signal, a precoding matrix from a codebook, where a precodingmatrix W included in the codebook is a product of three matrices beingW₁, Z, and W₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag{Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, β_(i,k)≥0;and X_(i) corresponds to Z_(i); and sending a precoding matrix indicatorPMI to the base station by using the transceiver 601, where the PMIcorresponds to the selected precoding matrix, and is used by the basestation to obtain the selected precoding matrix W according to the PMI.

The selecting, based on the reference signal, a precoding matrix from acodebook specifically includes:

selecting, based on the reference signal, the precoding matrix from acodebook subset, where the codebook subset is a subset predefined, ornotified by the base station, or reported by the user equipment.

Optionally, the codebook subsets share at least one same matrix subsetof the following matrix subsets: subsets of a matrix W₁, a matrix W₁Z, amatrix W₂, a matrix ZW₂, and a matrix Z.

Optionally, the sending a precoding matrix indicator PMI to the basestation by using the transceiver 601 specifically includes:

sending a first precoding matrix indicator PMI₁ and a second precodingmatrix indicator PMI₂ to the base station, where the PMI₁ is used toindicate the matrix W₁Z, and the PMI₂ is used to indicate the matrix W₂;or

sending a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ to the base station, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;or

sending a second precoding matrix indicator PMI₂, a third precodingmatrix indicator PMI₃, and a fifth precoding matrix indicator PMI₅ tothe base station, where the PMI₅ is used to indicate the matrix Z.

Optionally, the sending a precoding matrix indicator PMI to the basestation by using the transceiver 601 specifically includes:

sending the PMI₁ to the base station according to a first period; and

sending the PMI₂ to the base station according to a second period, wherethe first period is greater than the second period; or

sending the PMI₃ to the base station according to a third period; and

sending the PMI₄ to the base station according to a fourth period, wherethe third period is greater than the fourth period; or

sending the PMI₂ to the base station according to a second period;

sending the PMI₃ to the base station according to a third period; and

sending the PMI₅ to the base station according to a fifth period, wherethe third period is less than the second period and the fifth period.

Optionally, the sending a precoding matrix indicator PMI to the basestation by using the transceiver 601 specifically includes:

sending the PMI₁ to the base station according to a first frequencydomain granularity; and

sending the PMI₂ to the base station according to a second frequencydomain granularity, where the first frequency domain granularity isgreater than the second frequency domain granularity, for example,sending a wideband PMI₁ and a sub-band PMI₂ to the base station; or

sending the PMI₃ to the base station according to a third frequencydomain granularity; and

sending the PMI₄ to the base station according to a fourth frequencydomain granularity, where the third frequency domain granularity isgreater than the fourth frequency domain granularity, for example,sending a wideband PMI₃ and a sub-band PMI₄ to the base station; or

sending the PMI₂ to the base station according to a second frequencydomain granularity;

sending the PMI₃ to the base station according to a third frequencydomain granularity; and

sending the PMI₅ to the base station according to a fifth frequencydomain granularity, where the third frequency domain granularity is lessthan the second frequency domain granularity and the fifth frequencydomain granularity, for example, sending a wideband PMI₂, a widebandPMI₅, and a sub-band PMI₃ to the base station.

It should be noted that, the sizes of the foregoing wideband andsub-band may vary with the size of a system bandwidth. For example, in a10 MHz LTE system, the wideband may include 50 physical resource blocksRBs, and the size of the sub-band may be 6 consecutive RBs; and in a 5MHz LTE system, the wideband may include 25 RBs, and the size of thesub-band may be 3 consecutive RBs.

Optionally, the block matrix X_(i)=[X_(i,1) X_(i,2)], where each columnof the matrix X_(i,j) is selected from columns of a Householder matrix,a discrete Fourier transform matrix, a Hadamard matrix, a rotatedHadamard matrix, or a precoding matrix in an LTE R8 system 2-antenna or4-antenna codebook or in an LTE R10 system 8-antenna codebook.

Further, each column of the matrix X_(i,j), j=1,2 is separately selectedfrom columns of different Householder matrices, different discreteFourier transform matrices, different Hadamard matrices, differentrotated Hadamard matrices, or different precoding matrices in an LTE R8system 2-antenna or 4-antenna codebook or in an LTE R10 system 8-antennacodebook.

Optionally, the block matrix X_(i)=[X_(i,1) X_(i,2)], where the matrixX_(i,j) is a Kronecker product of two matrices being A_(i,j) andB_(i,j), and j=1,2.

Further, columns of the matrix X_(i,1) and the matrix X_(i,2) are columnvectors of a Householder matrix, a discrete Fourier transform matrix, aHadamard matrix, a rotated Hadamard matrix, or a precoding matrix in anLTE R8 system 2-antenna or 4-antenna codebook or in an LTE R10 system8-antenna codebook.

Optionally, W₁ is an identity matrix.

Optionally, a column vector in the matrix W₂ has a structure:y_(n)=γ⁻¹[e_(n) ^(T) e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) representsa selection vector, where in the vector, the n^(th) element is 1 and allother elements are 0; θ_(n) is a phase shift; and γ is a positiveconstant.

It should be noted that, apart from the precoding matrix having theforegoing structure, the codebook may further include other precodingmatrices, so as to meet requirements of other scenarios, which is notlimited herein.

In this embodiment of the present invention, user equipment determinesand sends a precoding matrix indicator PMI, where the PMI indicates aprecoding matrix, and the precoding matrix has a structure: W=W₁ZW₂,where both W₁ and Z are block diagonal matrices, and each column of eachblock matrix Z_(i) in the matrix Z has a structure:

$z_{i,k} = {{( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}.}$

For the precoding matrix, two column vectors (or referred to as beams)can be separately selected from each block matrix X_(i) by using theforegoing structure; and phase alignment and weighting are performed onthe two column vectors (or beams), where the two column vectors selectedfrom X_(i) may separately point to two major multipath transmissiondirections. Therefore, by using the foregoing structure, for each columnof an obtained matrix X_(i)Z_(i), interference between two majormultipath transmission directions can be converted into a wanted signal,and combining gains are obtained, thereby improving system transmissionreliability and a system transmission throughput.

Embodiment 5

This embodiment of the present invention provides a base station. Asshown in FIG. 7, the base station includes: a sending unit 71, areceiving unit 72, and a determining unit 73.

The sending unit 71 is configured to send a reference signal to userequipment UE.

The receiving unit 72 is configured to receive a precoding matrixindicator PMI sent by the UE.

The determining unit 73 is configured to determine a precoding matrix Win a codebook according to the PMI, where the precoding matrix W is aproduct of three matrices being W₁, Z, and W₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag {Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, β_(i,k)≥0;and X_(i) corresponds to Z_(i).

Optionally, the determining unit 73 is specifically configured todetermine the precoding matrix in a codebook subset according to thePMI, where the codebook subset is a subset predefined, or reported bythe user equipment, or notified by the base station.

The codebook subsets share at least one same matrix subset of thefollowing matrix subsets: subsets of a matrix W₁, a matrix W₁Z, a matrixW₂, a matrix ZW₂, and a matrix Z.

Optionally, the receiving unit 72 is specifically configured to:

receive a first precoding matrix indicator PMI₁ and a second precodingmatrix indicator PMI₂ that are sent by the UE, where the PMI₁ is used toindicate the matrix W₁Z, and the PMI₂ is used to indicate the matrix W₂;

or

receive a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ that are sent by the UE, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;

or

receive a second precoding matrix indicator PMI₂, a third precodingmatrix indicator PMI₃, and a fifth precoding matrix indicator PMI₅ thatare sent by the UE, where the PMI₅ is used to indicate the matrix Z.

Optionally, the receiving unit 72 is specifically configured to:

receive, according to a first period, the PMI₁ sent by the UE; and

receive, according to a second period, the PMI₂ sent by the UE, wherethe first period is greater than the second period; or

receive, according to a third period, the PMI₃ sent by the UE; and

receive, according to a fourth period, the PMI₄ sent by the UE, wherethe third period is greater than the fourth period; or

receive, according to a second period, the PMI₂ sent by the UE;

receive, according to a third period, the PMI₃ sent by the UE; and

receive, according to a fifth period, the PMI₅ sent by the UE, where thethird period is less than the second period and the fifth period.

Optionally, the receiving unit 72 is specifically configured to:

receive, according to a first frequency domain granularity, the PMI₁sent by the UE; and

receive, according to a second frequency domain granularity, the PMI₂sent by the UE, where the first frequency domain granularity is greaterthan the second frequency domain granularity, for example, a widebandPMI₁ and a sub-band PMI₂ are sent to the base station; or

receive, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receive, according to a fourth frequency domain granularity, the PMI₄sent by the UE, where the third frequency domain granularity is greaterthan the fourth frequency domain granularity, for example, a widebandPMI₃ and a sub-band PMI₄ are sent to the base station; or

receive, according to a second frequency domain granularity, the PMI₂sent by the LE;

receive, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receive, according to a fifth frequency domain granularity, the PMI₅sent by the UE, where the third frequency domain granularity is lessthan the second frequency domain granularity and the fifth frequencydomain granularity, for example, a wideband PMI₂, a wideband PMI₅, and asub-band PMI₃ are sent to the base station.

It should be noted that, the sizes of the foregoing wideband andsub-band may vary with the size of a system bandwidth. For example, in a10 MHz LTE system, the wideband may include 50 physical resource blocksRBs, and the size of the sub-band may be 6 consecutive RBs; and in a 5MHz LTE system, the wideband may include 25 RBs, and the size of thesub-band may be 3 consecutive RBs.

Optionally, the block matrix X_(i)=[X_(i,1) X_(i,2)], where each columnof the matrix X_(i,j) is selected from columns of a Householder matrix,a discrete Fourier transform matrix, a Hadamard matrix, a rotatedHadamard matrix, or a precoding matrix in an LTE R8 system 2-antenna or4-antenna codebook or in an LTE R10 system 8-antenna codebook.

Further, each column of the matrix X_(i,j) is separately selected fromcolumns of different Householder matrices, different discrete Fouriertransform matrices, different Hadamard matrices, different rotatedHadamard matrices, or different precoding matrices in an LTE R8 system2-antenna or 4-antenna codebook or in an LTE R10 system 8-antennacodebook.

Optionally, the block matrix X_(i)=[X_(i,1) X_(i,2)], where the matrixX_(i,j) is a Kronecker product of two matrices being A_(i,j) andB_(i,j), and j=1,2.

Specifically, columns of the matrix X_(i,1) and the matrix X_(i,2) arecolumn vectors of a Householder matrix, a discrete Fourier transformmatrix, a Hadamard matrix, a rotated Hadamard matrix, or a precodingmatrix in an LTE R8 system 2-antenna or 4-antenna codebook or in an LTER10 system 8-antenna codebook.

Optionally, W₁ is an identity matrix.

Optionally, a column vector in the matrix W₂ has a structure:y_(n)=γ⁻¹[e_(n) ^(T) e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) representsa selection vector, where in the vector, the n^(th) element is 1 and allother elements are 0; θ_(n) is a phase shift; and γ is a positiveconstant.

This embodiment of the present invention further provides a basestation. As shown in FIG. 8, the base station includes: a transceiver801, a memory 802, and a processor 803. Certainly, the base station mayfurther include common-purpose components such as an antenna and aninput/output apparatus, which is not limited herein in this embodimentof the present invention.

The memory 802 stores a set of program code, and the processor 803 isconfigured to invoke the program code stored in the memory 802, toperform the following operations:

sending a reference signal to user equipment UE by using the transceiver801; when the user equipment reports a PMI, receiving, by using thetransceiver 801, the precoding matrix indicator PMI sent by the UE; anddetermining a precoding matrix W in a codebook according to the PMI,where the precoding matrix W is a product of three matrices being W₁, Z,and W₂, that is, W=W₁ZW₂, where

both W₁ and Z are block diagonal matrices, W₁=diag{X₁, . . . , X_(N)_(B) }, Z=diag {Z₁, . . . , Z_(N) _(B) }, each of W₁ and Z includes atleast one block matrix, that is, N_(B)≥1, and each column of each blockmatrix Z_(i) in the matrix Z has the following structure:

$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}$

where [ ]^(T) represents matrix transposition; e_(i,k) represents ann_(i)×1 selection vector, where in the vector, the k^(th) element is 1and all other elements are 0, and n_(i) is a half of a column quantityof a block matrix X_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, β_(i,k)≥0;and X_(i) corresponds to Z_(i).

The determining a precoding matrix W in a codebook according to the PMIspecifically includes: determining the precoding matrix in a codebooksubset according to the PMI, where the codebook subset is a subsetpredefined, or reported by the user equipment, or notified by the basestation.

The codebook subsets share at least one same matrix subset of thefollowing matrix subsets: subsets of a matrix W₁, a matrix W₁Z, a matrixW₂, a matrix ZW₂, and a matrix Z.

The receiving the PMI by using the transceiver 801 may specificallyinclude: receiving a first precoding matrix indicator PMI₁ and a secondprecoding matrix indicator PMI₂ that are sent by the UE, where the PMI₁is used to indicate the matrix W₁Z, and the PMI₂ is used to indicate thematrix W₂;

or

receiving a third precoding matrix indicator PMI₃ and a fourth precodingmatrix indicator PMI₄ that are sent by the UE, where the PMI₃ is used toindicate the matrix W₁, and the PMI₄ is used to indicate the matrix ZW₂;

or

receiving a second precoding matrix indicator PMI₂, a third precodingmatrix indicator PMI₃, and a fifth precoding matrix indicator PMI₅ thatare sent by the UE, where the PMI5 is used to indicate the matrix Z.

The receiving the PMI by using the transceiver 801 may specificallyinclude: receiving, according to a first period, the PMI₁ sent by theUE; and

receiving, according to a second period, the PMI₂ sent by the UE, wherethe first period is greater than the second period; or

receiving, according to a third period, the PMI₃ sent by the UE; and

receiving, according to a fourth period, the PMI₄ sent by the UE, wherethe third period is greater than the fourth period; or

receiving, according to a second period, the PMI₂ sent by the UE;

receiving, according to a third period, the PMI₃ sent by the UE; and

receiving, according to a fifth period, the PMI₅ sent by the UE, wherethe third period is less than the second period and the fifth period.

The receiving the PMI by using the transceiver 801 may furtherspecifically include: receiving, according to a first frequency domaingranularity, the PMI₁ sent by the UE; and

receiving, according to a second frequency domain granularity, the PMI₂sent by the UE, where the first frequency domain granularity is greaterthan the second frequency domain granularity, for example, receiving awideband PMI₁ and a sub-band PMI₂ that are sent by the UE; or

receiving, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receiving, according to a fourth frequency domain granularity, the PMI₄sent by the UE, where the third frequency domain granularity is greaterthan the fourth frequency domain granularity, for example, receiving awideband PMI₃ and a sub-band PMI₄ that are sent by the UE; or

receiving, according to a second frequency domain granularity, the PMI₂sent by the UE;

receiving, according to a third frequency domain granularity, the PMI₃sent by the UE; and

receiving, according to a fifth frequency domain granularity, the PMI₅sent by the UE, where the third frequency domain granularity is lessthan the second frequency domain granularity and the fifth frequencydomain granularity, for example, receiving a wideband PMI₂, a widebandPMI₅, and a sub-band PMI₃ that are sent by the UE.

It should be noted that, the sizes of the foregoing wideband andsub-band may vary with the size of a system bandwidth. For example, in a10 MHz LTE system, the wideband may include 50 physical resource blocksRBs, and the size of the sub-band may be 6 consecutive RBs; and in a 5MHz LTE system, the wideband may include 25 RBs, and the size of thesub-band may be 3 consecutive RBs.

The block matrix X_(i)[X_(i,1) X_(i,2)], where each column of the matrixX_(i,j) is selected from columns of a Householder matrix, a discreteFourier transform matrix, a Hadamard matrix, a rotated Hadamard matrix,or a precoding matrix in an LTE R8 system 2-antenna or 4-antennacodebook or in an LTE R10 system 8-antenna codebook.

Further, each column of the matrix X_(i,j) is separately selected fromcolumns of different Householder matrices, different discrete Fouriertransform matrices, different Hadamard matrices, different rotatedHadamard matrices, or different precoding matrices in an LTE R8 system2-antenna or 4-antenna codebook or in an LTE R10 system 8-antennacodebook.

Optionally, the block matrix X_(i)=[X_(i,1) X_(i,2)], where the matrixX_(i,j) is a Kronecker product of two matrices being A_(i,j) andB_(i,j), and j=1,2.

Specifically, columns of the matrix X_(i,1) and the matrix X_(i,2) arecolumn vectors of a Householder matrix, a discrete Fourier transformmatrix, a Hadamard matrix, a rotated Hadamard matrix, or a precodingmatrix in an LTE R8 system 2-antenna or 4-antenna codebook or in an LTER10 system 8-antenna codebook.

Optionally, W₁ is an identity matrix.

Optionally, a column vector in the matrix W₂ has a structure:y_(n)=γ⁻¹[e_(n) ^(T) e^(jθ) ^(n) e_(n) ^(T)]^(T), where e_(n) representsa selection vector, where in the vector, the n^(th) element is 1 and allother elements are 0; θ_(n) is a phase shift; and γ is a positiveconstant.

It should be noted that, apart from the precoding matrix having theforegoing structure, the codebook may further include other precodingmatrices, so as to meet requirements of other scenarios, which is notlimited herein.

In this embodiment of the present invention, after receiving a precodingmatrix indicator PMI reported by user equipment, a base stationdetermines a precoding matrix according to the PMI, where the precodingmatrix has a structure: W=W₁ZW₂, where both W₁ and Z are block diagonalmatrices, and each column of each block matrix Z_(i) in the matrix Z hasa structure:

$z_{i,k} = {{( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k}^{T}}\end{bmatrix}}^{T}.}$

For the precoding matrix, two column vectors (or referred to as beams)can be separately selected from each block matrix X_(i) by using theforegoing structure; and phase alignment and weighting are performed onthe two column vectors (or beams), where the two column vectors selectedfrom X_(i) may separately point to two major multipath transmissiondirections. Therefore, by using the foregoing structure, for each columnof an obtained matrix X_(i)Z_(i), interference between two majormultipath transmission directions can be converted into a wanted signal,and combining gains are obtained, thereby improving system transmissionreliability and a system transmission throughput.

It should be noted that, for specific descriptions of some functionmodules in the base station and the user equipment that are provided inthe embodiments of the present invention, reference may be made tocorresponding content in the method embodiments, and details are notdescribed again in this embodiment.

As seen from the descriptions of the foregoing embodiments, it may beclearly understood by a person skilled in the art that, for the purposeof convenient and brief description, division of the foregoing functionmodules is used as an example for illustration. In actual application,the foregoing functions can be allocated to different function modulesand implemented according to a requirement, that is, an inner structureof an apparatus is divided into different function modules to implementall or some of the functions described above. For a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments, anddetails are not described herein again.

In the several embodiments provided in the present application, itshould be understood that the disclosed system, apparatus, and methodmay be implemented in other manners. For example, the describedapparatus embodiment is merely exemplary. For example, the module orunit division is merely logical function division and may be otherdivision in actual implementation. For example, a plurality of units orcomponents may be combined or integrated into another system, or somefeatures may be ignored or not performed. In addition, the displayed ordiscussed mutual couplings or direct couplings or communicationconnections may be implemented through some interfaces. The indirectcouplings or communication connections between the apparatuses or unitsmay be implemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected according toactual needs to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of the presentinvention may be integrated into one processing unit, or each of theunits may exist alone physically, or two or more units are integratedinto one unit. The integrated unit may be implemented in a form ofhardware, or may be implemented in a form of a software functional unit.

When the integrated unit is implemented in the form of a softwarefunctional unit and sold or used as an independent product, theintegrated unit may be stored in a computer-readable storage medium.Based on such an understanding, the technical solutions of the presentinvention essentially, or the part contributing to the prior art, or allor some of the technical solutions may be implemented in the form of asoftware product. The software product is stored in a storage medium andincludes several instructions for instructing a computer device (whichmay be a personal computer, a server, or a network device) or aprocessor to perform all or some of the steps of the methods describedin the embodiments of the present invention. The foregoing storagemedium includes: any medium that can store program code, such as a USBflash drive, a removable hard disk, a read-only memory (ROM, Read-OnlyMemory), a random access memory (RAM, Random Access Memory), a magneticdisk, or an optical disc.

The foregoing descriptions are merely specific implementation manners ofthe present invention, but are not intended to limit the protectionscope of the present invention. Any variation or replacement readilyfigured out by a person skilled in the art within the technical scopedisclosed in the present invention shall fall within the protectionscope of the present invention. Therefore, the protection scope of thepresent invention shall be subject to the protection scope of theclaims.

What is claimed is:
 1. A method for reporting channel state information,the method comprising: receiving a reference signal from a base station;selecting, a precoding matrix from a codebook based on the referencesignal, wherein each precoding matrix W meets W=W₁ZW₂, wherein W₁ is ablock diagonal matrix and meets W=diag{X₁, . . . , X_(N) _(B) }, eachblock matrix in W₁ has a plurality of rows and columns, Z is a blockdiagonal matrix and meets Z=diag {Z₁, . . . , Z_(N) _(B) }, each blockmatrix in Z has a plurality of rows and columns, N_(B)≥1, wherein eachcolumn z_(i,k) of each block matrix Z_(i) in the matrix Z has thefollowing structure:$z_{i,k} = {( {\alpha_{i,k}^{2} + \beta_{i,k}^{2}} )^{- \frac{1}{2}}\begin{bmatrix}{{\alpha_{i,k}e_{i,k_{1}}^{T}}\ } & {\beta_{i,k}e^{j\; \theta_{i,k}}e_{i,k_{2}}^{T}}\end{bmatrix}}^{T}$ wherein i is an index of the block matrix Z_(i), kis an index of the column z_(i,k), [ ]^(T) represents matrixtransposition, e_(i,k) ₁ is an n_(i)×1 selection vector in which the k₁^(th) element is 1 and all other elements are 0, e_(i,k) ₂ is an n_(i)×1selection vector in which the k₂ ^(th) element is 1 and all otherelements are 0, n_(i) is a half of a column quantity of the block matrixX_(i); θ_(i,k) is a phase shift, α_(i,k)≥0, and β_(i,k)≥0; and sending aprecoding matrix indicator (PMI) to the base station, wherein the PMIcorresponds to the selected precoding matrix.
 2. The method according toclaim 1, wherein one of α_(i,k) and β_(i,k) is
 0. 3. The methodaccording to claim 1, wherein W₂ is a matrix which has a plurality ofrows and is used to select one column vector in the matrix W₁Z.
 4. Themethod according to claim 1, wherein W₂ is a matrix which has aplurality of rows and is used to perform weighting combination on morethan one column vectors in the matrix W₁Z.
 5. The method according toclaim 1, wherein each column of each block matrix in W₁ is a DiscreteFourier Transform, DFT vector.
 6. The method according to claim 1,wherein all the block matrices in W₁ are the same.
 7. The methodaccording to claim 1, wherein each block matrix X_(i) in the matrix W₁has the following structure:X _(i) =A _(i) ⊗B _(i) wherein the matrix A_(i) has a plurality of rowsand columns and the matrix B_(i) has a plurality of rows and columns andthe matrix.
 8. The method according to claim 7, wherein each column inthe matrix A_(i) and the matrix B_(i) is a DFT vector.
 9. The methodaccording to claim 7, wherein the matrix A_(i) corresponds to thehorizontal direction of the array of the base station and the matrixB_(i) corresponds to the vertical direction of the array of the basestation; or the matrix A_(i) corresponds to the vertical direction ofthe array of the base station and the matrix B_(i) corresponds to thehorizontal direction of the array of the base station.
 10. The methodaccording to claim 1, wherein θ_(i,k)=0.
 11. The method according toclaim 1, wherein different block matrices in W₁ correspond to antennagroups of different polarizations or different locations.
 12. The methodaccording to claim 1, wherein the PMI comprises a second PMI₂, a thirdPMI₃ and a fifth PMI₃, and the second PMI₂ is used to indicate thematrix W₂, the third PMI₃ is used to indicate the matrix W₁, and thefifth PMI₃ is used to indicate the matrix Z.